Hydraulically-Actuated Explosive Downhole Tool

ABSTRACT

A downhole tool comprising a first section having an internal sidewall defining at least a portion of a flowpath, and a ported outer sidewall and an explosive having at least a portion within said first section. An annular portion has at least one chamber having an end positioned adjacent to the explosive and an inlet providing a communication path to said flowpath. A detonator assembly is located within each chamber proximal to the explosive such that detonation of the assembly causes detonation of the explosive. A firing pin is propelled toward the detonation assembly by providing communication between the chamber and the flow path, causing a pressure differential between the pressure isolated ends of the firing pin.

CROSS-REFERENCES TO RELATED APPLICATIONS

This continuation-in-part application claims the benefit of the filing date of U.S. application Ser. No. 13/777,134, filed Feb. 26, 2013, which is a continuation application claiming the benefit of the priority date of U.S. application Ser. No. 12/637,255 (now U.S. Pat. No. 8,381,807), filed Dec. 14, 2009, each of which are incorporated by reference as a part of this application.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND

The present disclosure relates to a well stimulation tool for oil and/or gas production. The embodiments described herein generally relate to an explosive stimulation downhole tool that may be hydraulically actuated and is for use in a hydrocarbon well.

DESCRIPTION OF THE RELATED ART

In hydrocarbon wells, fracturing (or “fracing”) is a technique used to create and/or extend a fracture from the wellbore deeper into the surrounding formation, thus increasing the surface area for flow of formation fluids into the well. Fracing may be done by either injecting fluids at pressures sufficient to overcome the compressive and cohesive forces on the formation of interest (hydraulic fracturing), by using explosives to generate sufficient pressure and gas flow (e.g. TNT or PETN at up to 1,900,000 psi), and or by using propellant stimulation. Fluids used in hydraulic fracturing may carry proppants, which are typically granular material such as sand or ceramic particles. Further, fracturing may be performed using a combination of these techniques.

Gas generating propellants have been utilized in combination with, in addition to, or in lieu of other fracturing techniques as a more cost effective manner to create and propagate fractures in a subterranean formation. In accordance with conventional propellant stimulation techniques, a propellant is ignited to pressurize a perforated subterranean interval either simultaneous with or after the perforating step so as to propagate fractures therein.

For example, U.S. Pat. No. 5,775,426 (issued Jul. 7, 1998, the “'426 Patent”), which is incorporated by reference herein, describes a perforating apparatus wherein a shell of propellant material is positioned to substantially encircle a shaped charge. The propellant material is ignited due to shock, heat, and/or pressure generated from a detonated charge. Upon burning, the propellant material of the '426 Patent generates gases that clean perforations formed in the formation by detonation of the shaped charge and which extend fluid communication between the formation and the well bore.

BRIEF SUMMARY

One embodiment of the downhole tool has a flowpath therethrough and includes a first section having an internal sidewall, an outer sidewall, and at least a portion of an explosive volume, such as a propellant volume, within the first section. At least one chamber may be disposed, such as in an annular portion, between the outer surface of the tool and the flowpath, with a first end of each chamber positioned adjacent to the propellant, or other explosive, volume. A detonator assembly may be positioned in one or more chambers proximal to the propellant, or other explosive, volume to, when actuated, ignite or cause ignition of the propellant or other explosive. Actuation of the detonator assembly is caused by impact of a primer by a firing pin, which is caused to move by the pressure differential between the flowpath and a portion of the chamber. Ignition of the propellant causes pressure waves to be directed radially away from the tool and into the surrounding formation.

Also according to one embodiment, a plurality of flow ports may be disposed through the exterior surface to provide for fluid flow into and out of the flowpath. A moveable sleeve assembly operates to prevent and permit fluid flow through the flow ports, depending on its position. In a first position, a sleeve substantially prevents fluid flow through the flow ports, while in a second position fluid flow is substantially permitted. The moveable sleeve also prevents or allows pressure communication between the flowpath and each chamber to cause application of a hydraulic force to the firing pin. The moveable sleeve may, in some embodiments, be a sleeve assembly comprising two, or more, sleeves joined by a connector such that the sleeves may move together. In some embodiments, the sleeve assembly may comprise two or more sleeves that are disengageable, such that, at a defined point in the sleeve assembly's movements, the sleeve's separate, allowing at least a first sleeve of the sleeve assembly to continue its movement while a second sleeve of the sleeve assembly remains stationary or, possibly, moves in a different direction than the first sleeve.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a partial sectional elevation of the preferred embodiment of the present invention.

FIG. 2 is a sectional elevation of a portion of the preferred embodiment more fully disclosing the middle sub and piston sleeve.

FIG. 3 is a sectional elevation through section line 3-3 of FIG. 2.

FIG. 4 is a sectional elevation through section line 4-4 of FIG. 2

FIG. 5 is a sectional elevation of a pressure chamber and firing pin of the preferred embodiment.

FIG. 6 is a sectional elevation of a portion of the preferred embodiment wherein the sleeve assembly is in a disengaged state in a second position.

FIG. 7 is a sectional elevation of the firing assembly and pressure chamber shown in FIG. 5 wherein the firing pin has been released and has impacted the primer.

FIGS. 8A-8B are a partial sectional elevation of an alternative embodiment of the present invention.

FIG. 8C is an enlarged view of window 8C in FIG. 8A.

FIG. 9 is an isometric view of the mandrel of FIG. 8.

FIG. 10 is a sectional elevation though section line 10-10 of FIG. 8.

FIG. 11 is an enlarged view of a pressure chamber and firing pin of the alternative embodiment as shown in FIG. 8A.

FIG. 12 is a sectional elevation of a portion of the alternative embodiment wherein the sleeve assembly is in a disengaged state in a second position.

FIG. 12A is an enlarged view of window 12A in FIG. 12.

FIG. 13 is an enlarged view of the pressure chamber and firing pin as shown in FIG. 12.

DETAILED DESCRIPTION

When used with reference to the figures, unless otherwise specified, the terms “upwell,” “above,” “top,” “downwell,” “below,” and “bottom,” and like terms are used relative to the direction of normal production through the tool and wellbore. Thus, normal production of hydrocarbons migrates through the wellbore and production string from the downwell to upwell direction without regard to whether the tubing string is disposed in a vertical wellbore, a horizontal wellbore, or some combination of both. In the figures, the arrow depicting flowpath 30 is pointing in the “downwell” direction (i.e., opposite the normal direction of fluid flow in the well during production).

FIG. 1 depicts a partial sectional elevation of one embodiment of the invention downhole tool, which comprises a first section 20 having a mandrel 22 with an internal sidewall 24 and a ported sleeve 26 having a ported outer sidewall 28. A flowpath 30 through the tool is partially defined by the substantially cylindrical internal sidewalls of the mandrel 22, a top connection 32, a middle sub 34, a ported housing 36, and a bottom connection 38. The mandrel 22 is threadedly attached to the top connection 32 and the middle sub 34 at its upper and lower ends, respectively. A cylindrical propellant volume 46 is adjacent to and between the mandrel 22 and the ported sleeve 26.

The ported sleeve 26 has a plurality of circular ports 40 spaced equally radially around the outer sidewall 28, and is attached to the top connection 32 with a plurality of low head cap screws 42. The bottom end of the ported sleeve 26 is attached to the upper end of the middle sub 34 with a series of interlaced tabs 44 positioned in slots 45 disposed in the outer surface of the middle sub 34.

A second section 48 of the tool includes a plurality of oblong flow ports 50 that define a fluid communication path between the flowpath 30 and the exterior of the tool. The flow ports 50 may be spaced around, and disposed through, the cylindrical ported housing 36, which has an upper end connected to the lower end of the middle sub 34 with a plurality of circumferentially-aligned grub screws 52, and a lower end threadedly attached to the bottom connection 38. Sealing rings 60 are positioned throughout the embodiment to prevent undesired fluid communication between the various elements, except through the flowpath 30 and through the plurality of flow ports 50.

A pressure chamber 54, such as a cylindrical pressure chamber, is disposed longitudinally through a chamber, such as annular portion 56, of the middle sub 34. A detonator assembly 58 and firing pin 90 are located within the pressure chamber 54, with the detonator assembly 58 located proximal to the upper end of the pressure chamber 54.

The middle sub 34 and ported housing 36 enclose a moveable sleeve assembly 62 having an attached ball seat 64, or other plug seat, for selectively allowing communication through the flow ports 50 to the surrounding formation, as will be described infra. The sleeve assembly 62 is, in the embodiment of FIG. 1, anchored in a first position by a plurality of circumferentially-aligned shear pins 66.

FIG. 2 is a sectional view of a portion of an embodiment including the middle sub 34 and sleeve assembly 62, which comprises a piston sleeve 68 coupled to an insert sleeve 70. The sleeve assembly 62 is moveable between a first position and a second position, wherein in the first position the sleeve assembly 62 prevents fluid communication between the flowpath 30 and the exterior of the tool through the flow ports 50. For example, in the first position, the upper end of the piston sleeve 68 abuts a bottom profile 72 of the middle sub 34 to define a portion of the flowpath 30. A first plurality of ports 74 provides a fluid communication path to the exterior of the piston sleeve 68. A radially contractible firing pin locking key 76 is disposed circumferentially around the piston sleeve 68.

A lower section of the piston sleeve 68 has a larger interior diameter than an upper section. In the first position, the upper end of the insert sleeve 70 initially abuts the shoulder 78 defining the top end of the second portion, and is coupled thereto with a circumferentially-positioned expandable piston locking key 80 or other bridging element. The insert sleeve 70 is initially secured to the ported housing 36 with shear screws 66. Upper and lower sealing rings 84, 86 are circumferentially disposed around the insert sleeve 70 to isolate the flow ports 50 from the flowpath 30, thus substantially preventing communication between the flowpath 30 and the exterior of the tool.

FIG. 3 is a sectional view through section line 3-3 of FIG. 2 more fully disclosing the positioning of the three pressure chambers 54 disposed longitudinally within the portion 56 of the middle sub 34, and showing first ends 88 of firing pins 90 (see FIG. 2), which, in FIGS. 2 and 3, are orientated in the upwell direction.

FIG. 4 more fully discloses the positioning of the shear screws 66 to secure the insert sleeve 70 to the ported housing 36. The flow ports 50 are spaced equally radially around the ported housing 36. The ball seat 64 defines an orifice 65 composing a portion of the flowpath 30.

FIG. 5 is a sectional view of the detonator assembly 58 and firing pin 90. The firing pin 90 is within pressure chamber 54 proximal to an inlet 55, and is retained in position by the firing pin locking key 76 engaged with a retention groove 100 circumferentially disposed around the firing pin 90. The first end 88 of the firing pin 90 is pressure isolated from the second end 89 with a sealing ring 102. The inlet 55 of each chamber 54 provides a fluid communication path to the flowpath 30.

The detonator assembly includes a primer 92, primer case 94, shaped charge 96, and an isolation bulkhead 98. The primer 92 is spaced above the firing pin 90 within the primer case 94. The shaped charge 96 is positioned above and adjacent to the primer case 94. The isolation bulkhead 98 is positioned adjacent the shaped charge 94 and proximal to the propellant volume 46. In this position, detonation of the shaped charge 94 will cause corresponding ignition of the propellant volume 46.

FIG. 6 is a sectional elevation of an embodiment wherein the sleeve assembly 62 comprising the piston sleeve 68 and insert sleeve 70 is in a second position to allow fluid communication between the flowpath 30 and the surrounding formation through the flow ports 50 of the ported housing 36. To shift the sleeve assembly 62 to this second position from the first position shown in FIG. 1, an appropriately-sized ball 104 or other plug is caused to flow down the wellbore and to engage the ball seat 64. Engagement of ball 104 with the ball seat 64 seals off the flowpath 30 to prohibit fluid flow in the downwell direction through the orifice 65. Thereafter, the well operator can cause the pressure within the flowpath 30 to exceed the shear strength of the shear pins 66 attaching (in the first position) the insert sleeve 70 to the ported housing 36, which causes the shear pins 66 to fracture and detach the insert sleeve 70. In FIG. 6, the shear pins 66 are shown in a sheared state.

After shearing the pins 66, increased fluid pressure within the flowpath 30 causes the insert sleeve 70 and piston sleeve 68 to move downwell until the lower section of the piston sleeve 68 contacts an inner shoulder 82 of the piston housing 36. In this position, the piston locking key 80 expands into an adjacent flanged section 81 and decouples the insert sleeve 70 from the piston sleeve 68. The insert sleeve 70 is thereafter allowed to continue downwell under the flowpath pressure until it contacts the bottom connection 38 (see FIG. 1). The ported housing 36 further includes a locking section 106 that engages a ratchet ring 108 circumferentially disposed around the insert sleeve 70 to prevent upwell movement of the insert sleeve 70 after moving into the locking section 106.

Movement of the sleeve assembly 62 to the second position causes hydraulic actuation of the firing pin 90 as follows. Engagement of the piston sleeve 68 with the interior shoulder 86 positions an outer groove 110 to allow the firing pin locking key 76 to radially contract thereinto. This contraction causes the firing pin locking key 76 to disengage from the firing pin 90.

As shown in FIG. 7, pressure communicated into the pressure chamber 54 causes the firing pin 90 to move towards the detonator assembly, upwell in FIG. 6, because of the pressure differential above and below the sealing ring 102. In other words, because pressure on the detonator assembly side of the sealing element 102 is atmospheric, hydraulic pressure on the opposing side of sealing element 102 applies a hydraulic force on the second end 89 of the firing pin 90 resulting in movement towards the detonator assembly.

FIG. 7 shows the detonator assembly 58 with the pressure chamber 54 after the firing pin locking key 76 has released the firing pin 90 and at the point of contact of the firing pin 90 with the primer 92. The sealing ring 102 between the first end 88 and second end 89 of the firing pin 90 isolates pressure in the pressure chamber 54 on the detonator assembly side of the sealing ring 102 from the pressure in the flowpath 30. After ports 74 are aligned with the inlet 55, pressure within the flowpath 30 is communicated through the ports 74 into the pressure chamber 54 at a position below the sealing element 102 (e.g. on the side opposite of the detonator assembly), resulting in a pressure differential that moves the firing pin 90 to contact and detonate the primer 92. Detonation of the primer 92 is contained by the case 94 and causes detonation of the adjacent shaped charge 96, which transfers explosive energy to the propellant volume 46, causing ignition thereof. The explosive energy is directed radially outwardly in the form of pressure waves through the circular ports 40 (see FIG. 1) and into the surrounding formation.

FIG. 8A and FIG. 8B together depict an alternative embodiment 112 having an upper end 114, a lower end 116, and a flowpath 115 extending through the embodiment 112 between the ends 114, 116. The embodiment 112 comprises a top connection 118, an outer sleeve 120 having a cylindrical outer sidewall 121, a middle sub 122, a nozzle housing 124, a lower housing 126, and a bottom connection 128. The outer sleeve 120 is connected to the top connection 118 with circumferentially-aligned screws 130. An upper end 132 of the nozzle housing 124 is connected to the lower end 134 of the middle sub 122 with a third group of circumferentially-aligned screws 136. The upper end 140 of the lower housing 126 is connected to the lower end 138 of nozzle housing 124 with circumferentially aligned screws 142. The lower end 144 of the lower housing 126 is connected to the bottom connection 128 with circumferentially aligned screws 146. The lower housing 126 has a generally cylindrical inner surface 147, a portion of which has annular ridges defining a locking section 149. Nozzle housing 124, as depicted in FIGS. 8A and 8B does not contain ports through which fluid may flow upon movement of the lower sleeve from a first position to a second position. However, it will be appreciated that such ports may be present and are envisioned as within the scope of present disclosure.

Referring specifically to FIG. 8A, the top connection 118 has an upper end surface 148, a lower end surface 150, and interior surfaces partially defining a flowpath that intersects with the tool flowpath 115. The interior surfaces may include a partially conical surface 152 adjacent to the upper end surface 148 and an adjacent cylindrical surface 154. An inner shoulder surface 156 is positioned between the upper and lower end surfaces 148, 150 and adjacent to the surface 154.

The middle sub 122 has an upper end surface 158 and an lower end surface 160. A cylindrical outer surface 161 extends between the upper end surfaces 158 and a shoulder surface 163. The middle sub 122 may have a varying inner diameter defined by a cylindrical upper inner surface 162, a cylindrical intermediate surface 164, and a cylindrical lower inner surface 166. An annular upper intermediate shoulder surface 168 is adjacent to and between the intermediate surface 164 and the upper inner surface 162. A lower intermediate shoulder surface 170 is adjacent to and between the intermediate surface 164 and the lower inner surface 166. In the embodiment of FIG. 8, the intermediate surface 164 partially defines flowpath 115.

Mandrel 172 occupies a portion of the interior of the tool, such as a portion of the top connection 118 and the middle sub 122 as shown in FIG. 8. The mandrel 172 may be fixed relative to top connection 118, middle sub 122, or both. The mandrel 172 has an upper end surface 174, an lower end surface 176, and a cylindrical internal sidewall 178 adjacent to and extending between the upper and lower end surfaces 174, 176 that defines a portion of the flowpath 115. A cylindrical outer surface 182 (shown in FIG. 9) extends from the upper end surface 174 to a shoulder surface 175 near the lower end surface 176.

The mandrel 172 is inhibited from translational and rotational movement relative to the top connection 118 and middle sub 122. For example, circumferentially-aligned screws 180 may fix the mandrel 172 to the top sub 118. Further, the upper end surface 174 may be in contact with the inner shoulder 156 of the top connection 118, 186 the lower end surface 176 may be in contact with the upper shoulder 168 of the middle sub 122, or both. A first section 177 of the embodiment 112 includes at least part of the internal sidewall of the mandrel 172 and at least part of the outer sidewall.

FIG. 9 is an isometric view of the mandrel 172, which may be a generally tubular body having an outer surface 182. The mandrel 172 may include a circumferential groove 184 near the upper end surface 174. Longitudinal grooves 186 may extend along the outer surface 182 between the circumferential groove 184 and the shoulder surface 175. Charge receptacles, such as cylindrical recesses 188 are placed along and in communication with the longitudinal grooves 186. The number, placement, and spacing of charge receptacles may vary based on the results desired by the operator. Explosives, such as shaped charges 187, occupy some or all of the charge receptacles formed in the mandrel 172, with at least some charges being positioned within the first section 177.

A detonator cord 259 is fastened to each of the shaped charges 187 and extends along one longitudinal groove 186 a, into the circumferential groove 184, and into the next longitudinal groove 186 b, around the shoulder surface 175 and into the next longitudinal groove (not shown), and so on. In this manner the detonator cord 259 may occupy one or more of the grooves 186. One end of the detonator cord 259 is fastened to the detonator assembly 258, as shown in FIG. 8A.

Referring back to FIG. 8A, a moveable sleeve assembly may be comprised of a pin sleeve 190 and a lower sleeve 202 and defines a portion of the flowpath 115. The pin sleeve 190 has an upper end surface 192, a lower end surface 194, a cylindrical inner surface 196 adjacent to and extending between the end surfaces 192, 194, and an outer surface 198 adjacent to the end surfaces 192, 194. The upper end surface 192 contacts the lower shoulder surface 170. In some embodiments, the pin sleeve 190 may comprise a pin sleeve coupler element, such as groove 200 shown in FIG. 8 circumscribing the sleeve 190 proximal to the lower end surface 194.

Referring jointly to FIGS. 8A-8B, the lower sleeve 202 is adjacent to and in communication with pin sleeve 190. The lower sleeve 202 has an upper end surface 204 in contact with the lower end surface 194 of the pin sleeve 190, and an annular lower end surface 206. A cylindrical inner surface 208 and a generally cylindrical outer surface 210 extends between the upper end surface 204 and lower end surface 206. In some embodiments, the outer surface 210 may include a lower sleeve coupler element, such as the groove 212 that circumscribes the lower sleeve 202 near the upper end surface 204 in the embodiment illustrated in FIG. 8B. The outer surface 210 also may include shear pin receivers such as recesses 214 for receiving an end, such as the shearable ends 216, of pins 218.

In certain embodiments, the downhole tool may contain a bridge assembly for connecting the pin sleeve and lower sleeve. In some embodiments, the bridge assembly releasably connects the pin sleeve and lower sleeve such that the pin sleeve and lower sleeve may be disconnected at a desired time or in response to a predetermined event. Referring to FIG. 8C, one embodiment of a bridge assembly comprises a collet ring 219 configured to engage the groove 200 of the pin sleeve 190 and groove 212 of the lower sleeve 202. The collet ring 219 has a body 221 with a lower end surface 223 and a cylindrical outer surface 225. In the embodiment of FIG. 8C, a plurality of fingers 227 may extend from the body 221 and occupy the groove 200 in the pin sleeve 190, terminating in upper end surfaces 229. The body 221 circumscribes, and occupies the groove 212 defined by, the lower sleeve 202. The lower end surface 223 is adjacent to the outer surface 225. The body 221 has a cylindrical inner surface 233 and upper and lower partially-conical surfaces 235, 237 adjacent to the inner surface 233. The lower partially-conical surface 235 is also adjacent to the lower end surface 223. It will be appreciated that the configuration of the collet ring 219, when present, may be modified in numerous ways, and that the claims are not limited to any particular configuration of collet ring 219. Further, bridge assemblies of varying configurations, including bridge assemblies that do not include a collet ring, are within the scope of the present disclosure. One example of such a bridge assembly may comprise a locking assembly described in U.S. patent application Ser. No. 13/694,509, incorporated herein by references, modified such that the ball or other bolt connects the sleeves and allows the lower sleeve to pull the pin sleeve until the ball or bolt reaches the recessed area and the sleeves can disengage.

Referring again to FIG. 8B, the lower sleeve 202 is engaged with a seat carrier 220 that has an upper end surface 222, a lower end surface 224, and a generally cylindrical outer surface 226 extending between the upper and lower end surfaces 222, 224. The carrier 220 has an upper shoulder surface 228 and a lower shoulder surface 230. In some embodiments, the lower sleeve 202, seat carrier 220, or other structure engaged to lower sleeve 202 and/or seat carrier 220 may include one or more retaining elements. For example, in the embodiment of FIG. 8B, such retaining element comprises a ratchet ring, shown residing in a groove 232 circumscribing the seat carrier 220.

A ball seat 236 may be threaded to the seat carrier 220. Plugs other than balls are within the scope of the present disclosure and the ball seat 236 may be substituted with any seat configured to seal with the desired plug, provided that the plug and plug seat fit within the geometry, both size and shape, of the downhole tool, and, in the case of plug, any structures in the well through which the plug must pass to reach the plug seat. The ball seat 236 has an upper end surface 238 adjacent to the lower end surface 206 of the lower sleeve 202, and a lower end surface 240 positioned adjacent to the upper intermediate shoulder surface 228 of the seat carrier 220. The ball seat 236 defines an orifice 242 intersecting the flowpath.

In some embodiments, a cement sleeve 244 is attached to the seat carrier 220 below the lower shoulder surface 230. The cement sleeve 244 may be a tubular body having an upper end surface 246 and a lower end surface 248. A cylindrical outer surface 252 is positioned adjacent to the lower end surface 248. A shoulder 254 is adjacent to and positioned above the outer surface 252.

An actuator, such as a detonator assembly 258, for actuating the charges 187 is placed adjacent to the grooves 186. For example, and referring back to FIG. 8A, a chamber 256 is disposed longitudinally through a mandrel wall 250 of the middle sub 122 between the upper inner surface 162 and the outer surface 161. The detonator assembly 258 and a firing pin 260 are located within the chamber 256, with the detonator assembly 258 located near the upper end surface of the middle sub 122. The detonator assembly 258 and firing pin 260 are configured to match the shape and size of the chamber 256, which is cylindrical in certain embodiments. FIG. 10 shows one embodiment with three such chambers 256 positioned within the middle sub 122 in the mandrel wall 250. Alternative embodiments of my have more or fewer chambers. A detonator cord 259 is coupled to the detonator assembly 258 and occupies a longitudinal channel 186 formed in the mandrel 172.

Referring to embodiment shown in FIG. 11, the firing pin 260 occupies the chamber 256 near an inlet 262 extending between the lower inner surface 166 of the middle sub 122 and the chamber 256. The firing pin 260 has a first end 266 isolated from a second end 268 with a sealing ring 270 such that first end 266 and second end 268 are not in fluid communication. The chamber 256 is isolated from the flowpath 115 with a sealing element 261 a positioned between the pin sleeve 190 and the middle sub 122. A second sealing element 261 b may also isolate the chamber 256 from fluid in flowpath 115.

A retaining pin 264 may be connected to the firing pin 260, such as the retaining pin 264 shown in FIG. 11 between the sealing ring 270 and the second end 268. A portion of the retaining pin may occupy at least a portion of the inlet 262. In such a configuration, movement of the firing pin 260 within the chamber 256 substantially away from the position shown in FIG. 11 while the retaining pin 264 is intact is inhibited by the inlet wall 263.

A detonator assembly 258, such as illustrated in FIG. 11, may include a primer 272, primer case 274, shaped charge 276, and a bulkhead 278. The primer 272 is within the primer case 274 and is spaced between the firing pin 260 and at least one charge 187. The bulkhead 278 may be an isolation bulkhead positioned adjacent the shaped charge 276 and proximal to the mandrel 172. In this position, detonation of the shaped charge 276 will cause corresponding detonation of the charges 187 positioned in recesses 188 of the mandrel 172. The detonator cord 259 is fastened to the detonator assembly 258.

FIG. 12 is a sectional elevation of a portion of the embodiment wherein the pin sleeve 190 is downwell of the sealing element 261, which allows fluid communication between the flowpath 115 and the inlet 262. To shift the pin sleeve 190 to this position from the first position shown in FIG. 8A, an appropriately-sized ball 280 or other appropriate plug is caused to flow down the wellbore and to engage the ball seat 236 or other corresponding plug seat. In the embodiment of FIG. 12, engagement of the ball 280 with the ball seat 236 seals off the flowpath 115 to stop fluid flow through the orifice 242. Thereafter, the well operator can cause sufficient pressure to cause the ball seat 236, seat carrier 220, and lower sleeve 202 to move downwell. For example, according to the embodiment of FIG. 12, the fluid pressure in flowpath 115 is increased such that pressure differential across the ball seat 236, exceeds the shear strength of the shear pins 218, causing the shear pins 218 to fracture and detach the lower sleeve 202 from the nozzle housing 124.. In FIG. 12, the shear pins 218 are shown in a sheared state with ends 216 having moved relative to the position shown in FIG. 8A. Because the pin sleeve 190 is joined to the lower sleeve 202 with the collet ring 219, the pin sleeve 190 is also moved downwell.

In some embodiments, a bridge element between the pin sleeve and lower sleeve may disengage, break, or other otherwise disconnect such that the pin sleeve 190 and lower sleeve 202 no longer move together. For example, in the embodiment of FIG. 12, movement of the pin sleeve 190 is limited by contact of the lower end surface 223 of the collet ring 219 with an annular inner shoulder 127 of the nozzle housing 124. As pressure is applied after the collet ring 219 contacts the shoulder 127, the upper partially-conical surface 235 of the collet ring 219 allows the upper end surface 204 of the lower sleeve 202 to disconnect. In this manner, the lower sleeve 202 is disconnected from the pin sleeve 190 and may move in connection with the pressure differential across the ball seat 236. The lower sleeve 202 may thereafter move to the position shown in FIG. 12, in which ratchet ring 234 has expanded against, and engaged, the locking section 149.

Movement of the pin sleeve 190 to the second position shown in FIG. 12 allows pressure to thereafter be communicated from the flowpath 115 into the pressure chamber 256 through the inlet 262 and act on the second end 260 of the firing pin 260 and create a pressure differential thereacross. In other words, because pressure within the chamber on the detonator assembly 258 side of the sealing ring 270 is atmospheric, pressure on the opposite side of the sealing element 270 applies a force on the second end 268, causing movement of the firing pin 260 within the chamber 256 toward the detonator assembly 258. In embodiments having a retaining pin 264, or other firing pin restraint (for example, firing pin locking key, 76 in FIG. 2), the pressure from flowpath 115 must be high enough to apply sufficient force to the firing pin 260 to shear the retaining pin 264 as it contacts the inlet wall 263, or to otherwise disable, overcome, or deactivate a firing pin restraint configured to respond to the fluid pressure.

FIG. 13 shows the detonator assembly 258 with the pressure chamber 256 after the retaining pin 264 has sheared and at the point of contact of the firing pin 260 with the primer 272. The sealing ring 270 between the first end 266 and second end 268 of the firing pin 260 isolates pressure in the pressure chamber 256 upwell of the sealing ring 270 from the pressure in the flowpath 115. Detonation of the primer 272 is contained by the case 274 and causes detonation of the adjacent shaped charge 276, which ignites the detonator cord 259. Ignition of the detonator cord 259 detonates the charges 187 fastened thereto, and which are adjacent to the mandrel 172. The explosive resultant energy is directed radially outwardly through the outer sleeve 120 in the form of pressure waves and, desirably, into the surrounding formation.

In some embodiments, the number of longitudinal channels may exceed the number of detonator assembly, as illustrated for the embodiment shown in FIG. 9, showing six longitudinal channels and FIG. 10, illustrating the use of three detonator assemblies. During operation, activation of the primer 272 is followed by ignition of shaped charge 276, which may ignite the detonator cord 259 fasted to the charges 187. The detonator cord may be directed into multiple channels, such as by wrapping the detonator cord into grooves 184 as it exits a longitudinal channel 186, at and end of the mandrel. The detonator cord 259 can then be passed from groove 184 into a second longitudinal channel 186 and ignite the charges placed therein. In this manner, it is possible that a single primer 272 and detonator cord 259, could be used to initiate detonation of each of the charges 187 positioned in the mandrel 178.

The present invention is described above in terms of specific illustrative embodiments. Those skilled in the art will recognize that alternative constructions of such an apparatus can be used in carrying out the present invention. Other aspects, features, and advantages of the present invention may be obtained from a study of this disclosure and the drawings, along with the appended claims. 

We claim:
 1. A downhole tool for stimulating a hydrocarbon-producing formation, the downhole tool comprising: a first section having an internal sidewall defining at least a portion of a flowpath, and an outer sidewall; at least one explosive having at least partly within said first section; an annular portion with at least one chamber having an end positioned adjacent to said at least one explosive and an inlet; at least one detonator assembly within said at least one chamber proximal to said end; at least one firing pin within said at least one chamber, said at least one firing pin having a first end pressure isolated from a second end; at least one sleeve defining at least a portion of said flowpath and moveable between a first position and a second position, wherein in said first position said sleeve assembly is between the inlet of said at least one chamber and said flowpath.
 2. The downhole tool of claim 1 wherein at least a portion of said at least one explosive is between said internal sidewall and said outer sidewall.
 3. The downhole tool of claim 2 wherein said at least one detonator assembly comprises a isolation bulkhead proximal to said at least one explosive, a shaped charge adjacent said isolation bulkhead, a primer case adjacent said shaped charge, and a primer adjacent said primer case.
 4. The downhole tool of claim 1 further comprising a retaining pin connected to said firing pin and occupying a portion of said inlet.
 5. The downhole tool of claim 1 wherein said sleeve assembly comprises: a first sleeve having a first end surface, a second end surface, a cylindrical outer surface extending between said first end surface and said second end surface and defining a first groove circumscribing said first sleeve; a second sleeve having a first end surface, a second end surface, a cylindrical outer surface extending between said first end surface and said second end surface and defining a second groove circumscribing said second sleeve; and a collet ring occupying said first groove and said second groove.
 6. The downhole tool of claim 5 wherein in said first position said second sleeve is attached to said second section with a plurality of shear pins.
 7. The downhole tool of claim 1 further comprising a detonator cord connected to the detonator assembly and the at least one explosive.
 8. A downhole tool for stimulating a hydrocarbon-producing formation, the downhole tool comprising: a mandrel defining at least a portion of a flowpath; at least one explosive adjacent said mandrel; a sleeve adjacent said at least one explosive; at least one detonator assembly adjacent to said at least one explosive; at least one firing pin operable to contact said at least one detonator assembly, said firing pin having a first end pressure isolated from a second end; a housing; and a sleeve assembly moveable between a first position and a second position and defining a portion of said flowpath.
 9. The downhole tool of claim 8 wherein: said at least one explosive is circumferentially disposed around at least a portion of said mandrel; and said sleeve is circumferentially disposed around at least a portion of said at least one explosive.
 10. The downhole tool of claim 8 further comprising: an annular portion; at least one chamber disposed within said annular portion, said at least one chamber having an end longitudinally adjacent to said at least one explosive and an inlet; and wherein said at least one detonator assembly is located at said end of said at least one chamber. 